Biological air filter



FIG. 1 shows a perspective view of the design.

FIG. 2 shows a rear view of the design.

FIG. 3 shows a front view of the design.

FIG. 4 shows a left side view of the design.

FIG. 5 shows a right side view of the design.

FIG. 6 shows a top view of the design; and,

FIG. 7 shows a bottom view of the design.

The broken lines depict portions of the air filter that form no part ofthe claimed design.

The ornamental design for a biological air filter, substantially asshown and described.